The invention is used in optoelectronics and mainly in liquid crystal display devices, particularly used as converters of electrical information into optical information, in the real time processing of optical images and in analog displays.
More specifically, the invention relates to an active matrix display device incorporating a display material having an optical property. The optical property of the display material is e.g. opacity, a refractive index, transparency, absorption, diffusion, diffraction, convergence, etc. Moreover, said material can be an amorphous or crystalline, liquid or solid body.
FIGS. 1a and 1b respectively diagrammatically show a perspective of an embodiment of a known active matrix display device and the inner face of one of the walls of said device.
FIG. 1a shows a first and a second insulating walls 1,3 facing one another and which are kept spaced and sealed by a joint 5. Between said walls is placed a display material layer 7 having an optical property, said material e.g. being a liquid crystal film.
Over the inner face of one of the walls 1 (FIGS. 1a and 1b) are distributed n parallel row conductors, designated L.sub.i and m parallel column conductors designated C.sub.j, which intersect the row conductors, i and j being integers such that 1.ltoreq.i.ltoreq.n and 1.ltoreq.j.ltoreq.m, said row and column conductors carrying electric signals appropriate for exciting the display material 7 and generated by not shown addressing means.
At the intersection of each row conductor L.sub.i and each column conductor C.sub.j is provided a switch I.sub.ij, such as a field effect transistor connected by its gate to the row conductor L.sub.i and arbitrarily by its source and drain to the column conductor C.sub.j and to an electrode E.sub.ij.
Moreover, the inner face of the other wall 3 is covered by a conductive material serving as a counterelectrode 13, which is raised to a reference potential.
An image point A.sub.ij is defined by a capacitor formed by electrode E.sub.ij and counterelectrode 13, the material 7 inserted between these two electrodes forming the dielectric of the capacitor.
In order to select an image point A.sub.ij, onto the row conductor L.sub.i is passed an electric signal, which selects the on state of the group of transistors connected to said row conductor and in particular the on state of transistor I.sub.ij associated with said image point. This transistor then transmits to the electrode E.sub.ij to which it is connected, the electric signal coming from the column conductor C.sub.j. Between electrode E.sub.ij and counterelectrode 13 appears an electric field, which will bring about the excitation and collective orientation of the molecules of the display material placed between electrode E.sub.ij and counterelectrode 13, when the signal from column C.sub.j is equal to or greater than a threshold potential V.sub.S corresponding to the minimum value necessary for exciting material 7. This collective orientation will modify the optical property of the material at image point A.sub.ij.
By using the punctiform excitation of the liquid crystal, an image appears on the complete display device whilst defining it point by point.
Other types of active matrix display devices are known. Thus, e.g. FR-A-No. 2 553 218 describes an active matrix display device having on the inner face of one of its walls, a matrix of electrodes connected by switches to row conductors and on the inner face of the other wall, column electrodes facing the matrix of electrodes and connected to column conductors, the switches also being connected to a reference potential.
The number of image points of the known display devices is equal to the number of row conductors multiplied by the number of column conductors, or in other words n.m. Moreover, any increase in the number of image points in a known display device leads to an increase in the number of row and/or column conductors and therefore to an increase in the constructional complexity of the display device and to an increase in its inactive surface. The inactive surface corresponds to a surface not occupied by the matrix of electrodes of the device, each electrode of said matrix corresponding to an image point.